Television transmission tube



June 29, 1943. w. FLEcHslG TELEVISION TRANSMISSION TUBE Filed May l5, 1941 /u/Ia aannam vlranannal/L 'anavavuu11aaa. '1101111111111 lINVENTER R FLEcHsIG Patented June 29, 1943 2,323,024 TELEVISION TRANSMISSION TUBE Werner Flechsig,v Berlin-Charlottenburg, Ger- Ymany; vested in the Alien Property Custodian Application May 15, 1941, serial No. 393,602 In Germany May 29, 1940 (Cl. Z50-153) 4 Claims.

The invention relates to television transmission tubes of the charge storage type, and particularly to tubes in which an electron stream is controlled by charges applied to a charge storage electrode.

` `Atube of this type contains for instance a foraminous gridlike charge storage electrode carrying a mosaic of insulated photoelectric particles. This mosaic electrode is illuminated by the light of the television image so that the insulated particles acquire a positive charge. An additional source of electrons is arranged within the tube in such a manner that these electrons are directed in their movement towards the grid like electrodes. These electrons liberate upon the grid a number of secondary electrons of slow velocity and the passage of these slow electrons through the grid is controlled by the charged particles upon the grid. z

The known tubes of this type have however a drawback which decreases vtheir sensitivity. The experiments show namely that not only the slow electrons which are easily influencedV by the charges upon the mosaic are moving through the grid openings but that also fast primary electrons pass through the control grid and produce an unmodulated current at the signal electrode, which may be a vmultiple of the modulated image current. This unmodulated current 1s particularly large in case the secondary electrons are emitted by the backside of the charge storage electrode which is not illuminated by the light of the image and isnot photo-sensitive. In this `case a large number of primary electrons will ow through the'openings of the gridlike electrode and will arrive upon the signal electrode of the tube.

It has been suggested to make the signal elec- I trode cylindrical so that the cylinder is situated around the stream of electrons passing through the grid. With a suitable potential at the signal electrode, the slow controlled electrons shall be guided towards and collected by the signal elec# trode whereas the fast primary electrons move in axial direction and are collected by an electrode arranged vertically to the axis of the tube. In this manner it may be possible to collect the primary electrons but these electrons produce again secondary electrons at the collecting electrode and new disturbances are produced.

It is an object of the present invention to provide an electrode arrangement in which only the secondary electrons emitted by the charge storage electrode and controlled by the potentials of this electrode are collected by the output electrode.

It is a further object to provide a television transmission tube of high sensitivity and low unmodulated current. A further object is to separate `the modulated electrons from the unmodulatedv electrons by a simple electrode arrangement. p p

According tothe invention an electrode is arranged between the collecting electrode for the primary electrons and the signal electrode and this addition-al electrode has a negativepotential against the collecting electrode.

` O ther aspects of my invention will be apparent or will be specifically pointed out in the descripn tion forming a part of this specication, but I do not limit myself to the embodiment of the invention herein described, as variousv forms may be adopted within the scope of the claims.

.Referring to the drawing the figure shows a longitudinal section through a tube according to the invention. y

The tube I is an evacuated envelope having a plane window 2 at one end thereof. A transparent metal layer is applied to the inside of this window. Instead thereof a wire screen 3 may be arranged as collecting electrode near the window. `The other end of the tube contains an electron gun system 8, and a concentrating electrode 9. At this end of the tube, there are also pro vided a pair of deflecting coils l0, as shown; A mosaic electrode 4 is arranged in the path of the cathode ray produced by the electron gun system. This mosaic electrode ispermeable to electrons and has for instance the form of a screen or of a perforated foil. 'The side of the grid towards the window is covered with a large numberof insulated photoelectric particles. The mosaic electrode has a clean metal surface at the other side thereof and this surface may be made secondary emissive by applying suitable and known substances to these surfaces for instance caesium and caesium oxide. A cylindrical signal electrode 5 is arranged along the Wall of the tube on the side of the mosaic towards the window. This signal electrode collects the controlled electrons, A decelerating electrode 6 is arranged between electrode 5 and the metal layer 3. This electrode has according to the invention the property that it suppresses the passage of secondary electrons emitted. by the metal layer 3 towards the signal electrode. The signal electrode 5 has a potential which is approximately 20 volts positive against mosaic electrode 4. The metal layer 3 has a p0- tential of approximately -10 volts against the mosaic electrode and the decelerating cylinder 6 a potential of -30 volts against the mosaic @16C- trode.

If an optical image is thrown by means o-f a lens 'l through the metal screen 3 upon the mosaic electrode 4 the mosaic layer assumes a charge distribution corresponding to the optical image. If the rear side of the mosaic electrode 4 is scanned by a cathode ray the primary electrons of the ray will liberate secondary electrons and these slow secondary electrons are drawn through the openings of the mosaic electrode by the positive charges of the mosaic layer. In the space adjacent to the mosaic the electrode 4 has the highest positive potential. rIhe slow electrons moving through the openings of the mosaicV electrode are completely taken up by the signal electrode 5. The primary electrons moving into this space through the openings of the mosaic electrode pass through the space surrounded by electrode 5 and impact upon the metal screen 3 in consequence of their high initial Velocity. The secondary electrons emitted by the screen 3 can however no-t move towards electrode 5 on account oi the decelerating eld of electrode 6 having a potential which is 20 volts lower than that of metal screen' 3, so that all secondary electrons emitted by this layer fall back upon the plane of their origin. It is therefore completely avoided that primary electrons or electrons produced by the primary electrons reach the signal electrode. This has the advantage that the shot noise of the signals derived from electrode 5 is very low because the signal current has a very low D. C. component.

The invention is not limited to the embodiment represented in the figure. It is not necessary that electrode 5 has the form of a homogeneous metal cylinder. It may for instance have the form of a grid or netting and may be arrangedv as the rst grid of a secondary emission multiplier arranged behind said grid What I claim is:

1. A television picture signal generating tube comprising an apertured charge storage electrode having photosensitive particlesv deposited thereon and adapted to have an optical image focused thereon, an electron gun at one side of said electrode for directing a beam of electrons thereat to produce secondary electrons' upon impact therewith, an output electrode adjacent the other side of said storage electrode for receiving the secondary electrons passing through the apertures thereof, a collecting electrode also at the other side of said storage electrode for intercepting the primary electrons of said beam passing through said apertures of said storage electro-de, and a decelerating electrode adjacent said collecting electrode for retarding secondary electrons produced by electron impact with said co1- lecting electrode thereby to prevent said lastnamed secondary electrons from reaching said output electrode.

2. A television picture signal generating tube comprising an apertured charge storage electrode having photosensitive particles deposited thereon and adapted to have an optical image focused thereon, an electron gun at one side of said electrode for directing a beam of electrons thereat to produce secondary electrons upon impact therewith, a cylindrical output electrode adjacent the other side of said storage electrode for receiving the secondary electrons passing through the apertures thereof, a collecting electrode also at the other side oi said storage electrode for intercepting the primary electrons of said beam passing through said apertures of said storage* electrode, and a decelerating electrode diposed between said output electrode and said collecting electrode for retarding secondary electrons produced by electron impact with said collecting electrode thereby to prevent said last-named secondary electrons from reaching said output electrode.

3. A television picture signal generating tube comprising an apertured charge storage electrode having. photosensitive particles deposited thereon and adapted to have an optical image focused thereon, an electron gun at one side of said electrode for directing a beam of electrons thereat to produce secondary electrons upon impact therewith, an output electrode adjacent the other side of said storage electrode for receiving the secondary electrons passingk through the apertures thereof, a transparent collecting electrode disposed in the path of the light of said image and also at the other side of said storage electrode for intercepting the primary electrons of said beam passing through said apertures ofA said storage electrode, and a decelerating electrode adjacent said collecting electrode for retarding secondary electrons produced by electron impact with said collecting electrode thereby to prevent said last-named secondary electrons from reaching said output electrode.

4. A television picture signal generating tube comprising an apertured charge storage electrode having photosensitive' particles deposited thereon andr adapted to have an optical image focused thereon, an electron gun at one side of said electrode for directing a beam of electrons thereat to produce secondary electrons upon impact therewith, aA cylindrical output electrode at the other side of said storage electrode for receiving the secondary electrons pass-ing through the apertures thereof, a transparent collecting electrode in` the path of therlight of saidimage and also at the other side of said storage electrode for intercepting the primary electrons of said beam pass-4 ing through said apertures of said storage'electrode, and a cylindrical decelerating electrode adjacent said collecting electrode'for retarding secondary electrons producedby electronY impact with said collecting electrode thereby to prevent said last-named secondary electrons from reaching said output electrode, said electron gun,- said collecting electrode and said decelerating eIec-' trode being mounted on the same axis. 1

WERNER lE'LECIrISIG.v 

